The present invention relates to a timepiece with a device for controlling a stepping motor which includes an oscillator, a frequency divider connected to the said oscillator in order to produce a plurality of control signals and a control circuit which is connected at least indirectly to the said frequency divider for delivering driving pulses to the said motor.
In electronic timepieces which include a stepping motor, it is useful to be able to match the energy of the driving pulses to the motor load in such a way as to achieve the lowest possible power consumption while retaining full reliability of operation. Known systems, for example, use an excess motor load detector which can be used to alter the duration or the amplitude of the average driving pulses to a higher value when excess load is detected. Other systems use an unperformed step detector by means of which additional higher energy compensating pulses are emitted when an unperformed step is detected. These, in fact, are safety systems which can be used merely to deliver extra energy when such is needed. The driving pulses are therefore not matched at all times to the motor load. More advanced systems, which also use an unperformed step detector, can be used to determine periodically the operating limit of the motor by progressively reducing the energy of the driving pulses. When an unperformed step is detected the energy of the driving pulses is fixed at a value which is slightly higher than the limit found so as to ensure that the motor operates with sufficient reliability. This limit of course depends on the motor load, so that on average the energy of the impulses is matched to the motor load. This matching process is slow however. In fact, the system requires the periodic emission of compensating signals which consume energy, which is contrary to the intended aim. In order to minimise this defect, the operating limit can only be determined at well spaced intervals, and the energy of the driving pulses cannot be matched to rapid changes in load which occur between two determinations of the limit. Here again the system does not permit matching to the motor load to be effected continuously and rapidly.